1. Field of the Invention
The present invention relates to a histogram stretching apparatus and a histogram stretching method.
2. Description of the Related Art
In general, image contrast refers to a difference between a bright area and a dark area in an image, that is, a magnitude of a contrast ratio therebetween. An image with a large contrast ratio may be considered to be an image having high contrast. An image having high contrast may be considered to be an image having an excellent degree of definition, due to a clear difference between bright areas and dark areas in the image. Therefore, when an image having low contrast is subjected to image processing so as to be converted into an image having high contrast, the degree of definition of the corresponding image is improved, thereby obtaining a high-quality image.
As an image processing technique for improving the degree of definition of an image having low contrast, a technology of stretching a histogram of an image is known. The frequency of an image having high contrast is widely distributed over each image level of the histogram. That is, the frequency of an image having high contrast is appropriately present, even in the bright area and the dark area, such that the frequency of the histogram of the image having high contrast is widely distributed over the overall image level. On the other hand, a difference between bright areas and dark areas in an image having low contrast is small, such that the frequency of the histogram is distributed over a relatively narrower area of the image level. When the frequency distributed over the narrow area in the histogram of the image having low contrast is corrected so as to be widely distributed, an image having a large difference between the bright areas and the dark areas thereof may be generated. As such, widely expanding the frequency distribution of a histogram may be referred to as histogram stretching.
In order to calculate the histogram, there is a need to calculate the frequency of the input image level. In order to calculate the frequency of the input image and store the calculated histogram, an operation logic and storage device in proportion to the size and depth of the input image is required. That is, when the input image is an 8-bit image of 640×480 size, 640×480×28 registers are required, such that the size of the storage device may be increased and the number of operations of the operation logic may be increased.
To resolve the above defects, a method of reducing the size of the input image at a certain ratio or reducing the depth information thereof has been proposed, but may cause distortion of the input image, such that accurate histogram calculation results may not be derived therefrom.
Patent Document 1 of the following Related Art Documents relates to an apparatus and a method of stretching a histogram capable of improving contrast of an image. However, Patent Document 1 does not disclose a method of reducing a size of a storage device and a number of operations of operation logic.